Excerpt: In his charge to Lewis & Clark, Jefferson included, “Observe the soil & face of the country, its growth & vegetable productions; especially those not of the U.S. The animals of the country generally, and especially those not known in the United States; the remains of any which may be deemed rare or extinct…the dates at which particular plants put forth or lose their flower or leaf; times of appearance of particular birds ,reptiles, or insects.” These observations, according to Jefferson, were to “be taken with great pains & accuracy; to be entered distinctly, & intelligibly for others as well as yourself…” It is this emphasis on scientific matters that distinguishes this expedition.